Field
The present invention relates to forming organic thin films by vapor deposition.
Description of the Related Art
Organic thin films have valuable optical, thermal, electrical and mechanical properties and are widely used in the electronics, medical engineering, defense, pharmaceutical, and micro- and nanotechnology industries. Polymers in the microelectronics and photonics industries include, among other examples, photon- or electron-curable/degradable polymers for lithographic patterning; and polyimides for packaging, interlayer dielectrics and flexible circuit boards. Norman et al., Annu. Rep. Prog. Chem., Sect. C, 2005, 101, 174-201.
Polyimide films in particular are valuable for their thermal stability and resistance to mechanical stress and chemicals. Polyimide thin films can be used as a starting point in semiconductor applications for amorphous carbon films or layers, which are needed for future V-NAND structures. Polyimide films can be used, for example, as antireflection layers to improve pattern definition and reduce misalignment in lithography steps, as layers in multiple patterning (e.g., SDDP, SDQP), as insulating materials for interlayer dielectric materials, or as the gate dielectric in all-organic thin film transistors.
Polymer thin films have traditionally been fabricated through spin-coating techniques. The spin-coating method forms highly functional polymer films by coating a rotating disc with a liquid material and sintering the liquid. However, tailoring of spin-applied films is limited for several reasons. For instance, formation of uniform thin films on a substrate is difficult to control, in part because of the viscosity of the starting liquid, and it can be difficult to fill the gaps of very small features (e.g., trenches or gaps between metal lines) without void generation after curing. Also, spin-coating over high topography relative to the desired thickness of the layer can result in discontinuous and non-conformal deposition. As semiconductor chip sizes continue to shrink, thinner and higher-strength films with more tunable morphology are required.
Recently, vapor phase deposition processes such as chemical vapor deposition (CVD), vapor deposition polymerization (VDP), molecular layer deposition (MLD), and sequential deposition processes such as atomic layer deposition (ALD) and cyclical CVD have been applied to the formation of polymer thin films. In CVD, a film is deposited when reactants react on a substrate surface. Gases of one or more reactants are delivered to one or more substrates in a reaction chamber. In thermal CVD, reactant gases react with one another on a hot substrate to form thin films, with the growth rate influenced by the temperature and the amount of reactant supplied. In plasma enhanced CVD, one or more reactants can be activated in a remote plasma generator or in situ. In ALD, a film is built up through self-saturating surface reactions performed in cycles. Vapor phase reactants are supplied, alternatingly and repeatedly, to the substrate or wafer to form a thin film of material on the wafer. In a typical process, one reactant adsorbs in a self-limiting process on the wafer. A different, subsequently pulsed reactant reacts with the adsorbed species of the first reactant to form no more than a single molecular layer of the desired material. Thicker films are produced through repeated growth cycles until the target thickness is achieved. Plasma enhanced variants of ALD, and hybrid ALD/CVD processes (e.g., with some overlaps of the reactants permitted) are also known.